A so-called integrated optical circuit, wherein optical devices such as a semiconductor laser (hereinafter sometimes referred to simply as LD), an optical modulation device and a photodiode (hereinafter sometimes referred to simply as PD) are integrated on a substrate and coupled with to each other via waveguides, aims at downsizing and stabilizing optical systems and improving the performance of the same. Thus studies have been energetically made on these integrated optical circuits as the technology in the next generation. In preparing such an integrated optical device, although preparation of each of the devices is important, the coupling between the optical devices is the most important factor, and an increase in the optical coupling efficiency is desired. In a conventional optical coupling, however, the size and shape of a light exit face of an LD or an optical fiber and the refractive index of on optical fiber would not generally agree with those of a waveguide device (or these factors of the light exit end face of a waveguide would not agree with those of the light entrance end face of the optical fiber or PD). It is therefore theoretically difficult to increase the optical coupling efficiency. Even if the size of the light exit face and refractive index of the optical fiber are approximated closely to those of a waveguide device, fine adjustment is required in order to couple the light exit face of the optical fiber with the light entrance face of the waveguide at a high accuracy in a space. This troublesomeness makes such a waveguide device expensive.
A number of attempts have been made to improve the optical coupling efficiency of such a waveguide device [see, for example, Y. Cai, T. Mizumoto, E. Ikegami and Y. Naito, Lightwave Technol., vol. 9, No. 5 (1991) pp 577-583; Y. Cai, T. Mizumoto and Y. Naito, Trans. IEICE, vol. E71, No. 10, (1988) pp 931-933; Japanese Patent Application Laid-open (Kokai) No. Hei-4-398803; Japanese Patent Application Laid-open (Kokai) No. Hei-4-240809; Japanese Patent Application Laid-open (Kokai) No. Sho-63-94205; Japanese Patent Application Laid-open (Kokai) No. Sho-60-133408; Japanese Patent Application Laid-open (Kokai) No. Sho-63-163407; Japanese Patent Application Laid-open (Kokai) No. Hei-4-255270; Japanese Patent Application Laid-open (Kokai) No, Hei-5-173036; Japanese Patent Application Laid-open (Kokai) No. Hei-5-63216; Japanese Patent Application Laid-open (Kokai) No. Hei-4-283704;
R. G. Hunsperger, "Springer Series in Optical Sciences, Integrated Optics: Theory and Technology", Second Edition (Springer-Verlag 1985) p. 102]. However detailed analysis indicates that no optical coupling with a high efficiency can be achieved in general under the conditions described in these references. At present, therefore, neither any highly effective optical coupling method which exhibits a resistance to the deviation in the positions of a light exit face of an LD or an optical fiber and a light entrance face of the waveguide nor requirements for such a method have been found.